The present invention relates to a sheet discharging device of an image forming apparatus which discharges a transfer sheet on which an image has been fixed.
With reference to FIGS. 5, 6(a) and 6(b), a sheet discharging device of an image forming apparatus will be explained as follows which forms an image by means of electrophotography.
Referring to FIG. 5, a photoreceptor belt 1 is provided around rotating rollers 2 and 3. When the rotating roller 2 is driven in the arrowed direction, the photoreceptor belt 1 is rotated clockwise. A charger 6, an exposure section composed of a laser writing system unit 7 and 4 developing units 8-11 accommodating 4 kinds of color developers, are sequentially disposed between a cleaning unit 13 located on the right side of the apparatus and a transfer unit 12 located on the left side as shown in FIG. 5. When the operation of charging, exposing and developing is repeated 4 times, a color toner image is formed on the photoreceptor belt 1, and then the color image is transferred onto a transfer sheet which has been sent from a sheet cassette 14. After the transfer operation has been completed, the surface of the photoreceptor belt 1 is cleaned by the cleaning unit 13. After that, the next image is formed by the same image forming process as that described before.
A toner image transferred onto a transfer sheet is fixed by a fixing roller 18.
The transfer sheet on which the toner image has been fixed, is discharged face-down onto a tray by a discharging device, the toner image side being located downward, or face-up, the toner image side being located upward.
Face-down discharging is usually applied to sheet discharging devices. The reason is: when each process from image formation to sheet discharge is sequentially carried out, transfer sheets are naturally discharged in the manner of face-down discharge. Face-up discharge is applied to sheet discharging devices when image quality must be checked, or when enlarged or reduced images are formed which must be checked by an operator.
When a transfer sheet is discharged face-down, a guide member 60 is operated so that the transfer sheet on which an image has already been fixed, is guided in the direction of a passage 621, and discharged onto tray 201 on cover 20 by discharging roller 191. When a transfer sheet is discharged face-up, the guide member 60 is operated so that the transfer sheet on which an image has already been fixed, is guided in the direction of a passage 622, and discharged onto a tray 202 on the image forming apparatus by a discharging roller 192.
FIGS. 6(a) and 6(b) are views showing circumstances of the sheet discharging device in the cases of face-down discharging and face-up discharging.
FIG. 6(a) shows circumstances in the case of face-down discharging.
When transfer sheets are discharged face-down, the tray 202 for face-up discharging is not necessary, so that the tray 202 is removed from the image forming apparatus, and the position in which the tray 202 has been disposed is covered with a cover 204. The guide member 60 can be rotated around a rotating shaft 61. When the guide member 60 is set as shown in FIG. 6(a), the transfer sheet on which an image has been fixed is guided in the arrowed direction so that it is guided to the passage 621, and discharged face-down onto the tray 201 by the discharge roller 191.
FIG. 6(b) is a view showing circumstances in which a transfer sheet is discharged face-up.
In the case of face-up discharging, the cover 24 provided in the upper portion of the image forming apparatus is opened, and the tray 202 is engaged with a stopper 203 so that it can be mounted in a predetermined position. Then, the guide member 60 is rotated around the rotating shaft 61 so that it can be set at the position shown in the drawing. When the aforementioned operations are completed, the transfer sheet on which a toner image has been fixed, is guided to the passage 622 in the arrowed direction, and discharged onto the tray 202 face-up
As explained above, it is not simple to change over between face-down discharging and face-up discharging. That is, it is necessary to conduct preparation work accurately. Practically, it is difficult to do the preparation work accurately. As a result, it is necessary to provide a protective cover or a safety device which is expensive.
For example, there is a possibility that the following disadvantages occur:
In the case of face-down discharging, the tray 202 for use in face-up discharging is not necessary, so that the tray 202 is removed. In the case where the cover 204 is not set after the tray 202 has been removed, various strange articles can enter the apparatus through the opening.
In order to prevent the disadvantages, it is necessary to provide a protective cover inside the apparatus. Alternatively, it is necessary to provide a safety device to interlock the cover 204 and the image forming apparatus which works in the following manner: unless the cover 204 is set, the image forming apparatus does nor work.
The following advantages also occur:
When the guide member 60 has been set so that transfer sheets can be discharged face-up, and when an operator has forgotten to open the cover 204, the transfer sheets drop into the apparatus. When the protective cover is provided in this case, the transfer sheets are jammed under the cover 204. When the cover 204 is opened and the operator has forgotten to set the tray 202, the same problems are caused. In order to prevent the aforementioned disadvantages, it is necessary to provide a safety device which works in the following manner: unless the tray 202 is set, the image forming apparatus does not work.
As described above, in the case of conventional face-down and face-up discharging, it is necessary to conduct preparation work as well as to provide a protective cover and safety device, which increases the cost.
Further, the present invention relates to an image forming apparatus which can discharge transfer sheets either face-down or face-up.
In general, transfer sheets on which an image has been transferred, are discharged outside of the apparatus face-up, because transfer sheets discharged face-up are convenient for checking the image quality in the case of continuous copying.
However, in a recording operation in which facsimile images are recorded by a laser type of image forming apparatus, it is not necessary to check the image quality each time a transfer sheet is discharged. Accordingly, it is advantageous to discharge transfer sheets face-down and put them in order.
In order to meet these requirements, an image forming apparatus is provided which can select between face-down and face-up discharging.
However, in the case of an image forming apparatus provided with a sorter which sorts discharged transfer sheets, it is difficult to change the direction of transfer sheets since the structure becomes complicated. Therefore, this type of image forming apparatus has not been realized yet.
According to Japanese Patent Application Open to Public Inspection No. 130355/1983, an image forming apparatus is proposed which can conduct two-sided copying. When images are formed by this apparatus on both sides of a transfer sheet, the transfer sheet is discharged with the first image formation side of the transfer sheet set downward. Therefore, this image forming apparatus can not accomplish the aforementioned object.
Further, the present invention relates to an image forming apparatus provided with a sorting device which collects and sorts transfer sheets onto which an image has been transferred.
According to a conventional electrophotographic image forming apparatus, an image forming operation is performed in the following manner: a document placed on a platen mounted on the upper surface of the image forming apparatus, is scanned by an exposing device; the scanned image is sent to a photoreceptor which is provided in the middle portion of the image forming apparatus, electrically charged and rotated at a constant speed so that the photoreceptor is exposed to the scanning light and a latent image is formed on the surface of the photoreceptor; the latent image is developed by a developing unit provided around the photoreceptor so that a visualized toner image is formed; the toner image is transferred onto a transfer sheet conveyed to the lower portion of the photoreceptor synchronously with image formation; the transfer sheet is conveyed to a fixing unit provided on the side of the photoreceptor so that the transferred image is fixed; the transfer sheet is discharged on a sorter which is provided on the side of the apparatus so that the transfer sheet is sorted in order; and finally the sorted transfer sheets are collected.
When a copy operation is performed by an operator in an electrophotographic image forming apparatus, especially in an electrophotographic copier, the apparatus is operated from the front. However, a sorter which sorts the copied sheets is vertically provided on the side of the apparatus, so that the operator must move from the front to the side to collect the copied sheets from the sorter. For that reason, it is inconvenient to handle the apparatus.
Further, the present invention relates to a color image forming apparatus which forms a color toner image on the surface of a belt-shaped image forming body, and transfers the image onto a transfer sheet.
There are various kinds of color image forming apparatus. In general, a color image forming apparatus is structured in the following manner:
A belt-shaped image forming body is provided around two rotating shafts; a plurality of developing units which accommodate toners of different colors, are disposed below the image forming body; while the photoreceptor belt is rotated a plurality of times, latent images, the number of which corresponds to that of the separated colors of a document image, are formed, and then developed by the developing units; and the formed color image is transferred onto a transfer sheet which is supplied from a cassette provided in a cassette chamber located under the developing units.
The photoreceptor belt of a color image forming apparatus is different from a photoreceptor drum. The photoreceptor belt can be curved around a roller, the radius of curvature of which is small. Accordingly, the photoreceptor belt can be made flat as a whole, so that the space can be used effectively. Further, when a separation electrode to separate a transfer sheet is provided in the portion where the radius of curvature is small, the transfer sheet can be positively separated from the photoreceptor belt. A group of developing units are stacked above the cassette chamber, and the photoreceptor belt is disposed on the group of developing units. A transfer sheet passage and a transfer sheet supply means which connects the cassette chamber with the transfer section of the photoreceptor belt, are provided along the side inner wall so that they do not interfere with the group of developing units. On the other hand, an opening through which the cassette is inserted, is formed in the side wall of the apparatus opposite to the transfer sheet supply passage and the supply means. Therefore, the transfer sheet cassette can be inserted into the cassette chamber in the same direction as the transfer sheet supply.
However, when the transfer sheet cassette is inserted into the cassette chamber from the opposite side to the transfer sheet passage and the transfer sheet supply means, it is necessary to structure the apparatus so that both side walls can be opened, because one side must be opened for jam clearance and the other side must be opened for supplying transfer sheets to the cassette. Therefore, a wide space is needed for installation of the apparatus, and further it is disadvantageous from the viewpoint of operation and maintenance.
In order to improve the aforementioned problems, it is desired to provide an image forming apparatus in which the transfer sheet inserting opening is formed on the same side as the transfer sheet passage so that jam clearance and maintenance can be carried out from the front of the apparatus.
However, in the image forming apparatus structured in the aforementioned manner, the mechanism to move and withdraw the transfer sheet supply means becomes complicated since the transfer sheet cassette inserting direction is opposite to the transfer sheet supply direction.
In the case of an apparatus which accommodates a plurality of cassettes, it is necessary to provide a guide member to guide upward a transfer sheet conveyed out from the lower cassette, so that this guide member must be concurrently moved and withdrawn when the cassette is attached to and detached from the apparatus. Accordingly, the mechanism becomes further complicated.
Further, a sorter provided on the upper portion of the transfer sheet guide is desirably operated from the same side of the image forming apparatus.